The present invention relates generally to thermostats used to control heating and cooling systems, such as gas or electric forced air furnaces, gas or electric radiant heating furnaces, electric forced air air-conditioning systems, and electric heat pumps. Invention may also be suitable for other types of systems, including solar and solar electric heating and cooling systems. While many systems provide both heating and cooling, the invention is suitable for use with systems that provide heating or cooling or both heating and cooling, often collectively referred to as a heater/cooler.
Programmable thermostats typically use a screen, such as a liquid-crystal display (LCD), to display both operational functions and programming values. The user enters commands into the thermostat, such as for setting the current time and date and programming the thermostat, by pressing keys or pressing appropriate positions on a touch screen display. Programming conventional thermostats is often accomplished by selecting a series of different screens on the display. In addition to making entries using a touch screen display, thermostat often include additional button type inputs.
High energy efficiency of buildings is often achieved in part by substantially reducing air infiltration into the building. One of the drawbacks of such tightly constructed buildings is that the air inside the building can become stale and often permits buildup of harmful or at least objectionable components in the air. The advantages that can be achieved by using controlled amounts of ambient, outside air to reduce these air quality problems when heating or cooling the building are well known. Some conventional systems cycle the air in the building or permit outside air to be introduced into the building at periodic intervals, such as for five minutes every hour, or by a special air purge cycle, typically when the building is not occupied. Other conventional system may permit the heater/cooler to incorporate a chosen percentage of outside air into the air being heated or cooled. See, for example, U.S. Pat. Nos. 2,372,839; 4,018,266; and 6,491,094. An exemplary thermostat is the Robertshaw model 9914i made by Invensys Controls of Carol Stream, Ill.